1. Field of the Invention
The present invention relates to an optical writer for writing an image by illumination to an optical-write-type display recording medium laid with a display layer and photoconductive layer having a memory nature, and more particularly to a multi-level optical writer for writing a multi-level image to an optical-write-type recording medium having a binary gray-level characteristic.
2. Background Art
Recently, attentions are drawn to the display recording medium having both the merits of electronic display and paper (also termed as an electronic or digital paper) besides paper mediums and electronic display devices, as a display recording medium.
Because this display recording medium possesses a memory nature as to display, write energy is satisfactorily provided by an image writer only during rewriting its information wherein there is no need of energy for maintaining the display. Accordingly, after writing information, the display recording medium solely is to be separated from the image writer so that it can be conveniently carried, piled up and arranged or held in the hand to read information.
The display recording mediums having memory natures as above include a known optical-write-type display recording medium capable of visibly and erasably storing an image by light illumination and voltage application and optical writer for writing an image to the display recording medium (see JP-A-2001-301233).
In the optical-write-type display recording medium described in JP-A-2001-301233, a liquid-crystal layer and a photoconductive layer, whose resistance is to be changed by light illumination, are laid between one pair of transparent electrodes. Meanwhile, in the optical writer for writing an image to the display recording medium, a two-dimensional light pattern is illuminated from an LCD (liquid-crystal display) panel to a photoconductive layer of the display recording medium through a two-dimensional micro-lens array in a manner focused thereon, thereby causing a resistance distribution based on the light pattern on the photoconductive layer. By applying a voltage to between the transparent electrodes through an electricity receiver, a divisional voltage based on the resistance distribution over the photoconductive layer is applied to the liquid crystal, thereby recording an image on the liquid-crystal layer in accordance with the divisional voltage distribution.
According to this optical writer, printing is possible by making a lighting of image information two-dimensionally while applying a voltage to the one pair of electrodes entirely. A large capacity of image information can be written at high speed, as compared to line-based lighting or scan-based lighting.
Also, there is also known a liquid-crystal display adapted for multi-level writing to a display recording medium thus enabling multi-level display (see JP-A-7-77703).
This display device employs a display recording medium having one pair of transparent electrodes at the inside of one pair of transparent electrode, between which provided are a first-carrier injection layer, a photoconductive layer and a second-carrier injection blocking layer. By a gray-level controller operating based on a signal representative of an image multi-level concentration, an lighting device is driven to generate modulated output light. With the output light, the photoconductive layer is lighted to obtain a high resolution and correct gray-level representation.
However, in the liquid-crystal display device, lighting is with a correction by the gray-level controller such that the non-linearity in the light transmissivity characteristic on the dimmer layer of the display recording medium turns into a linearity. Thus, application is impossible to a structure not having a dimmer layer.
FIGS. 14A to 14C show a light intensity distribution, during lighting, on a display recording medium structured not having a dimmer layer. The display recording medium 144 of this kind has a binary γ-characteristic (gray-level characteristic) shown in FIG. 14B. As shown in FIG. 14B, on an lighting surface 143 receiving the emission light 142 from a pixel 143 of an lighting panel 141, the resulting intensity distribution is rectangular in form sharply attenuated at peripheral regions even in case the emission light 142 is intensity-modulated.
In the case intensity modulation is done for the emission light of from the pixels of the lighting panel 141, the maximum level in the intensity distribution increases or decreases but there is no significant change in the area itself at a threshold E1 level required in printing. As a result, there is no change in the optical dot (image dot) size on the optical-write-type display recording medium 144. As shown in FIG. 14C, the optical dot 145a based on weak lighting and the optical dot 145b based on intense lighting are equivalent in size, making it impossible to form a gray-level image.
However, according to the conventional multi-level optical writer, gray-level representation is not available on the optical-write-type display recording medium having a binary gray-level characteristic even in case illumination is with an intensity-modulated lighting because of no change in optical spot size.